Apparatus for amplifying electric oscillations



C. T. JACOBS July 19, 1932.

APPARATUS FOR AMPLIFYINQG ELECTRIC OSCILLATIONS 2 Sheets-Sheet 1 Filed July 26, 1930 0w Frequency QQEKQ S Fig. 11

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C. T. JACOBS July 19, 1932.

APPARATUS FOR AMPLIFYING ELECTRIC OSCILLATIONS Filed July 26, 1930 2 Sheets-Sheet 2 My fi'equency INVENTOR. Cake, TVZwJv ATTORNEY Patented July 19, 1932 UNITED STATES PATENT OFFICE CHARLES T. JACOBS, F CHATHAM, NEW JERSEY, ASSIGNOR TO THOMAS A EDISON, IN CORPORATED, OF WEST ORANGE, NEW JERSEY, A CORPORATION OF NEW JERSEY APPARATUS FOR AMPLIFYING ELECTRIC OSCILLATIONS Application filed July 26,

This invention relates to apparatus for amplifying electric oscillations and more particularly to radio frequency amplifying systems employing amplifying vacuum tubes and designed to operate, without readjustments, over a relatively wide band of frequeneies.

My invention has for its object the production of an improved amplifying system of lo the class described, suitable to. be used in single or multistage form or in either form in association with other types of amplifying systems, characterized by the fact that each stage is highly efficient in amplification between its inferior and superior cut-01f frequencies.

Another object is to provide such an amplifying system by which different frequencies within the band between the cut-ofi fre- 2 quencies will be amplified with a highly satisfactory degree of uniformity.

A further object of my invention is to provide such an amplifying system suitable for production in quantity without the necessity for extractinglimits onthe electrical characteristics of its components. Other and allied objects will more fully appear from the following specification and the appended claims.

In the detailed description of my invention hereinafter set forth, reference is had to the accompanying drawings, of which Figure I is a diagrammatic view of a single stage amplifier embodying my invention in one form; v

Figure II is a typical amplification-frequency characteristic of such a stage of amplification under certain conditions Figure III is a diagrammatic view of a single stage amplifier embodying my invention in a slightly modified form;

Figure IV is a diagrammatic View of a single stage amplifier embodying my invention in another modified form;

Figure V is a similar View illustrating a modification in shielding of certain components of my invention; and Figure V1 is a typical amplification-frequency characteristic of a stage of amplifica- 1930. Serial No. 470,788.

tion embodying my invention under certain and 1n general preferred conditions.

In the past it has been customary in securing radio frequency amplification overa wide band of frequencies without readjust ments to couple the amplifying vacuum tubes employed, each to its successor or to any other succeeding work circuit, such as a vacuum tube detector or crystal detector circuit,

by means of a single transformer, having primary and secondary windings very tightly coupled to each other. Associated with the primary inductance of such a transformer are its own distributed capacity, the output capacity of the preceding vacuum tube and stray capacities produced by the wiring, shielding and the like. Similarly associated with the secondary inductance of such a transformer are its owndistributed capacity, 1

the input capacity of the .succeeding vacuum tube or other work circuitand other stray capacities. By. virtue of these capacities associated with the windings two tightly coupled resonant circuits are formed.

A suitable measure of the amplifying merit of such a system is the ratio between the amplified voltage at the input. of the tube or otherwork circuit following the transformer and the voltage, to be amplified, on the grid of the tube preceding the transformer. This ratio may be termed the amplification per stage'and, for a stage employing the trans former described, provided the natural resonant frequencies of the primary and ,sec-

sistance-reactance ratio, the coupling coeffident and the frequency.

It may be shown that the effective value of this function, if K is greater than N, is at a minimum of two values of F; that its value rises sharply at frequencies higher than the higher and lower than the lower of these two values of F that it is at a maximum at a frequency intermediate these two values of F and that if N and K remain constant with varying values of F the two minimum values of the function are equal.- Theterms minimum and -ma Ximum -are herein used in their differential sense as denoting values at which the first derivative of the function with respect to frequency changes its and not in the sense of single absolute greatest and least values. Since this function appears in the denominator of (1), a system of this character tends to have two peaks of amplification separated by a valley, or re gion of lower amplification, and accompanied by sharp cut-offs at frequencies slightly outside the band-between the two peaks. The higher frequency peak, however, tends to be of a much lower order than thelower fre-- quency peak, due to the F term in the de nominator of (1'), which term denotes discrimination against'amplification at higher frequencies.

To overcome or reduce this discrimination it is common practice to introduce capacity between the primary andsecondary windings of the transformer and to wind or connect the secondary in reversed direction with respect to the primary. This effects a form t of'capacitive coupling between theprimamf and secondary circuits of a nature which favors amplification at the higher frequencies, which amplificationffor practical purposes is additive to the amplification expressed by :(1), the total amplification becoming'th'erefore less affected by the F term in (1). "Other common practice is to wind the primary and/or secondary with wire of relatively'highi resistance and/or to introduce iron or like material into the field of the coils. This practice greatly increases the minimum values of the function f N, K, F)

byits effect onN without greatly increasing the'niaximum value, thus reducing the dis parity between the amplification of thesystem at the peak frequencies and the amplification at intermediate frequencies. It furthermore may be madeto an extent to cause the valueof'N and thereby the value of the function f (N,;K, F) to be appreciably great er at the-low frequency peak than at the high,

further reducing'the disparity in amplification at 'thetwo peak frequencies. In the practice of'my invention I employ, instead" of a single transformer, two transformers and a capacity, disposed in such a manner as to couple a vacuum tube to a succeeding vacuum tube orother work circuit in cascade througha system comprising three resonant circuits; for example, as shown in secondaries S and S andprimary-secondary capacities C and O respectively, the transformers being in non-inductive relation to each other.'fTheanon-inductive relation may be produced, if desired, by shields or cans B and B these'being connected to the cathode systems of tubes V and V as at points Y and Y or to some pointor points substantially of the same radio frequency potential as such cathode systems. G rep resents the total capacity in shunt to the primary P of transformer T comprising the distributed capacity of the winding P the output capacityof the tube V parallel stray capacities as to the shield;B ,"and

physicallyintroduced capacityqif "desired.

Similarly C represents the total capacity in shunt to the secondary S of the transformer T C is a condenser, forming,,with S and P a closed resonant circuit, V shown is an amplifyingvor detecting tubehaving input electrodes F and G ll being its cathode, and such source, B of input elec trode D; C. potentialdiife'rence aslmay be required for proper, operationfof-the ,tube

V Itwill be understood, however, that may comprise any other form of work circuit, such as a crystal (detector circuit. v

If the three resonant circuits C P S C P and S C have thejsame nat ural frequency, if P equals S andthe induce tance of each is noted by L, and if K de- 4 notes a similar coupling coefficient both of circuit 0 1 to circuit S .C -P and of circuit S C P to circuit Sa -G the'per wherein the significance of the symbolsis the shown thatifN remain constant with stage amplification is given approximately varying values of F, the two maximum val-V ues of the function are equal, the highest and lowest frequency minimum values of the function are equal and the middle frequency minimum is the lowest value to which the function attains. Thus a system of this characters tends to have three peaks of amplification, shown as 11, 13 and 15 in the typical or illustrative curve of Figure II, the middle frequency peak 13 being the highest, separatedby amplification valleys 12 and 14 and accompanied by sharp cut-offs occurring slightly outside the band between peaks 11 and 15. The less efiicient amplification at valley 1% and peak 15 than at valley 12 and peak 11, respectively, is due to the F term in the denominator of I have found it desirable in the practice of my invention to wind the transformers of moderately high resistance wire, such as fine copper wire, for the purpose of reducing generally the disparity of amplification between the peaks 11, 13, 15 and the valleys 12, 14, as well as for the purpose of reducing to a degree the disparity of amplification between the'valleys 12 and 14; and between the peaks 11 and 15. I have further found it desirable to utilize inherent capacity C, between the primary and secondary of transformer T5 together withwinding or connection reversal of the secondary S of this transformer with respect to the primary P I have found, however, that the effect ofprimary-secondary capacity C in transformer T is of a very much lower order than that of capacity C in transformer T but that in order to obtain a slight beneficial result from the use of this capacity the secondary S of the transformer T should be neither wound nor connected, or else should be both wound and connected, in reversed direction with respect to the primary P It should be noted that to obtain best results from the use of either C or C or both, the circuit S C P should be connected to the cathode systems of tubes V and V as by the connection in Figure I between points Z and X, or to any other point in the system which is substantially of the same radio frequency potential as such cathode systems. 7

In Figure III, I show an alternative arrangement wherein auto-transformers U and U 'are substituted for the true transformers T and T of Figure I. Othersym- 1 hole have the same significance in the two figures. It will be understood, of course, that combinations of one trueand one autotransformer may also be used as shown, for example, in Flg. I 1, in which figure the true transformer is shown as preceding the autotransformer.

In Figure V, I show two auto-transformers as in Figure III, excepting that they are not shielded from each other by separate shields, being positioned in substantially non-inductive relation to each other and being wound, if desired, in such relation on a common winding form. A single shield, shown as B,may be used around both, if desired. It will be understood, of course, that two true combinations of one trueand one autotransfo-rmer may be similarly utilized without separate shielding. In either Figure III, Figure IV or Figure V the basic; circuit arrangements and the analyses are the same as in Figure I, excepting for the omission of C, and/or O in arrangements using two auto-transformers or one auto-transformer, respectively. p

In many cases it is desirable to employ one or two auto-transformers for structural or economic reasons, in which cases the benefit of the use of C. and/or C is, of course, lost. I have further found that in many cases wherein one or two true transformers are used the benefits to be desired from the use of Cl and/or G with the appropriate direction of winding and/or connection of the secondaries as outlined above, are insufficient or otherwise unsatisfactory as a meansof overcoming discrimination in general against the, amplification of higher frequencies, which manifests itself particularly in low amplifi cation in valley 14. I have found thatin such cases greater uniformity of low and high frequency amplification may be secured over a given band by resonating two of the circuits to a slightly higher frequency and. the remaining circuit to" a lower'frfequenoy than that one frequency to which each cir cuit would be resonated in the case of similar natural periods for all three. 7 When this is done it is distinctly preferable to raise slightly the frequencies of circuits C P and S G and to lower that of the middle circuit S C P due tothe reduced. degree to which the constants of the middle circuit affect the amplification characteristics.

Such shifting of circuit frequencies maybe made to change the curve of the systemfrom one of the type of Figure II to one of the type of Figure VI, a more symmetrical and a preferable curve, of higher minimum amplification. I

' It may be shown that the stiffness, or total inductance-capacity ratio, of the middle circuit is almost without effect on the amplification characteristics. In this respect the mid dle circuit is unlike the first and thirdcire cuits, each of which should, for maximum for that reason it is desirable to use rela spectively given approximately by tively low inductance values for both S and P maintaining the natural frequency of circuit S C P at the frequency desired by the (qse of a relatively high capacity value If all three circuits separately have the same natural frequency F the frequencies of peaks 11, 13 and 15 in Figure II are re- This assumes similar coupling coefficients, each K between the first and middle circuits and between the middle and third circuits. Thus the frequencies of the extreme peaks and as a result thereof the cut-off frequencies are determined for any given natural frequency F by the coupling co-efiicients. If one of the circuits, however, and in particular the middle circuit, be resonant to a somewhat lower frequency than the other two, control of the natural frequency of this circuit produces a marked control of the frequency of the low'frequency'peak 11 and an appreciable control of the frequency of the peak 15, both of these frequencies shifting in the same direction with any change of the natural frequency of the middle circuit. I have found that by proper control ofthe value of G and preferably by utilizing therefor a capacity adjustable within limits the frequency response band of the system may readily be shifted over small ranges. This is'very desirable in quantity production of systems for the amplification of radio frequencies over wide bands as it permits less exacting manufacturing tolerances for the values of the component parts. I

It will be understood that although I have shown anddescribed my invention in single stage form, as many stages thereof as desired may be used, in combination, if further de sired, with other types of amplifying stages. It will'be further understood that changes Y F0 and may be made in the physical and electrical choice and disposition of components and of the precise manner of employment thereof, without departing from the scope or spirit ofthe appended claims.

I claim r 1.111 asystem for the amplification of radio frequency currents in combination a vacuum tube,,a succeeding workcircuit and coupling means connected in the output circuit of "said vacuum tube and to the input of said succeeding work circuit for coupling aid tube and said work circuitin cascade,-

which two have substantially the same resonant: frequency and the. other a substan tially'diiferent resonant frequency, whereby with fixed adjustments of all elements there'- of amplification may be secured over a wide band of frequencies. f I

2. In a system for the amplification of radio'frequency currents in combination a vacuum tube, a succeeding Work circuit and coupling means connected in the output circuit of said vacuum tube and to the input of said succeeding work circuit for coupling said tube and said work circuit in cascade,

said coupling means comprising, with the output capacity of vacuum tube and the input'capacity of said work circuit, three tight 1y coupled cascaded resonant circuits, of which two have substantially the same resonant frequency and the other a substantially lower resonant frequency, whereby with fixed adjustments of all elements thereof amplification maybe secured over a Wide band of frequencies. 7

3. In a system for the amplification of radio frequency currents in combination a vacuum tube, a succeeding-work circuit and coupling means connected in the output circuit of said vacuum tube and-to the input of said succeeding work circuit for coupling saidtube and said work circuit in cascade,

of said vacuum tubeand to the input of said succeeding work circuit for coupling said tube and said work circuit in cascade, said coupling means comprising, with the output capacity of vacuum tube and the input capacity of said work circuit, three tightly coupled cascaded resonant circuits, of which the first and last have substantially the same resonant frequency and the middle circuit a substantially lower resonantfrequency, whereby with fixed adjustments of all elements thereof amplifi cation may be secured overa. wide band of frequencies; V

"5'. In a system for the amplification of radio frequency currents in combination a vacuum tube, a succeeding work circuit and coupling means connected in the output circuit of said vacuum tube and to the input of said succeeding work circuit for coupling said tube and said work circuit in cascade, said coupling means comprising, with the output capacity of vacuum tube and the input capacity of said work circuit, three tightly coupled cascaded resonant circuits, of which the first and last are characterized by a relatively high inductance-capacity ratio and have substantially the same resonant frequency and the middle circuit is characterized by a relatively low inductance-capacity ratio and has a substantially lower resonant frequency than that of the first and third circuits, whereby with fixed adjustments of all elements thereof amplification may be secured over a wide band of frequencies.

6. In a system for the amplification of radio frequency currents in combination a vacuum tube, a succeeding work circuit and coupling means connected in the output circuit of said vacuum tube and to the input of said succeeding work circuit for coupling said tube and said work circuit in cascade, said coupling means comprising twotransformers in substantially non-inductive relation each to the other, each having tightly coupled primary and secondary windings, said transformers having one terminal of one winding of each connected together and having the opposite terminals of said windings connected through a capacity to produce three cascaded resonant circuits, at least one of said transformers having capacity between the primary and secondary windings thereof and the secondary of the second transformer in the cascade being reversed with respect to the primary thereof, whereby with fixed adjustments of all elements thereof amplification may be secured over a wide band of frequencies.

7. In a system for the amplification of radio frequency currents in combination a vacuum tube, a succeeding work circuit and coupling means connected in the output circuit of said vacuum tube and to the input of said succeeding work circuit for coupling said tube and said work circuit in cascade, said coupling means comprising one auto-transformer of a high degree of coupling and one transformer having tightly coupled primary and secondary windings in substantially noninductive relation to said auto-transformer said transformer having one terminal connected to said auto-transformer directly and having the other terminal of said winding connected to said auto-transformer through a capacity to produce three cascaded resonant circuits, the transformer following the autotransformer in the cascade and having capacity between the primary and secondary windings thereof and the secondary of the transformer being reversed with respect to the primary thereof, whereby with fixed adjustments of all elements thereof amplification may be secured over a wide band of frequencies. v

This specification signed this 24th day of July, 1930.

CHARLES T. JACOBS.

CERTIFICATE OF CORRECTION.

Patent No. 1,867,746. July 19, 1932.

CHARLES T. JAG OBS.

It is hereby certified that error appears in the printed specification of the above numbered-patent requiring correction as followsz" Page 1, line 25, for "extracting" read exacting; page 2, line 3; for "of" firs'roccurrence read for; line 24, for "low'er"-second occurrence read low; and line 123, before the article "a" insert the word at; page 3, lines 6 and 7, for "characters" read character; and line 71, for the words "combinations of" read transformers or; and that the said Letters Patent should he read. with these corrections therein that the same may conform to the record of the case in the Patent Office.

Signed and sealed this 29th day of November, A. D. 1932.

M. J. Moore, (Seal) Acting Commissioner of Patents. 

